This invention relates generally to an open end spinning machine, and more particularly to the prevention of the occurrence of snarls in the yarn end present in a yarn take-up tube at the time when the spinning machine stops or starts to operate.
Generally, in an open end spinning machine such as, for example, described in U.S. Pat. No. 3,354,626, each spinning unit includes means for feeding individually opened fibers into a spinning rotor, in which subatmospheric pressure is produced by rotation thereof. The opened fibers are formed into a yarn in the spinning rotor. The yarn is transported from the spinning rotor by a take-up means including a yarn take-up tube and yarn take-up rollers and is wound on a bobbin by a winding means. Also, in the above open end spinning machine, each of the fiber feeding means, yarn take-up means and yarn winding means is mounted on a separate driving shaft and a single motor drives these separate driving shafts through a rotation transmission mechanism including trains of gears. This motor also drives an endless belt, which is in frictional contact with spindles of the spinning rotors to rotate the same.
When the spinning machine is stopped, the fiber feeding means is first stopped to discontinue the supply of fibers to the spinning rotor, the take-up roller and winding roller are then stopped at a time when the yarn end resulting from breakage of the yarn still remains in the yarn take-up tube which undergoes the suction effect of the subatmospheric pressure in the spinning rotor. Finally, all the spinning rotors are stopped. On starting, all the spinning rotors start to rotate simultaneously, the yarn take-up rollers and winding rollers are then rotated in a reverse direction to push the yarn ends from the take-up tubes into the spinning rotors, while the fiber feeding means are operated to supply the opened fibers into the spinning rotors thereby to allow them to be twisted into the reversed yarn ends. Thereafter, the take-up rollers and winding rollers are rotated in a normal, yarn winding direction.
With this stopping method, the rotation of the spinning rotors continues for a predetermined period of time even after the take-up rollers have stopped, and the rotating rotors can impose the suction effect thereof upon the yarn ends in the yarn take-up tubes. This causes each yarn end to be untwisted between the associated spinning rotor and take-up rollers so that the occurrence of snarls in the yarn end can be prevented to some extent. However, where the yarn end has been given a strong twist, the afore-mentioned suction effect of the spinning rotor may not satisfactorily prevent the yarn end from being snarled after the stop of rotation thereof and therefore the yarn end may shrink upwardly out of the yarn take-up tube. In such case, even when the spinning rotor is rotated before the rotation of the take-up roller and winding roller starts in the reverse direction, it is not possible to introduce the yarn end into the take-up tube and hence to the spinning rotor by the suction effect of the latter. Moreover, in the spinning machine as discussed above, since the untwisting of the yarn end is intended to be effected between the spinning rotor and the yarn take-up rollers, the length over which the yarn end is untwisted is such that yarn quality is adversely affected.
It is therefore a principal object of this invention to provide a method and apparatus for starting and stopping an open end spinning machine, which can significantly prevent the occurrence of snarls in the yarn end regardless of the degree of twist of the yarn and can limit the untwisted length of the yarn to a favourable value.